Utilization of full spectrum space in single-sensor-based optical dynamic measurement

In recent years, interferometry-based dynamic measurement has been widely used in industrial area for noncontact measurement of vibration or continuous deformation. In dynamic measurement, the traditional phase extraction method, phase shifting technique, is not easily accomplished with either high-speed camera or single-pixel photo detector. Hence spectrum analysis becomes a predominant method to extract transient phases. Due to the development of high-speed cameras and photo detectors, now it is possible to encode different information at separated positions in spectrum. In this paper, we will present two applications on fully utilizing spectrum space in dynamic measurement. One is a dual-wavelength image-plane digital holography using high-speed camera, and another is a spatially encoded multi-beam laser Doppler vibrometry using a single detector. The former experiment encodes information of two wavelengths at different parts of the spectrum. Two phase maps can be retrieved from one hologram. These two phase maps can generate a new phase distribution with an equivalent wavelength, so that the capturing rate of the camera can be reduced dramatically. The latter application encodes vibration information of different points on separated frequency ranges. The experiment verifies it is possible to do a precise vibration measurement on a 2×5 matrix simultaneously using a single photo detector. These results show with fully utilization of spectrum space, the capability of optical dynamic measurement will be tremendously improved.